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Weekly Report: Influenza Summary Update

Week ending December 8, 2001-Week 49

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The following information may be quoted:

Synopsis:

During week 49 (December 2-8, 2001)*, 11 of 943 respiratory specimens tested by WHO and NREVSS laboratories were positive for influenza. The overall proportion of patient visits to sentinel physicians for influenza-like illness (ILI) was 1,2 %, which is less than the national baseline of 1,9 %. The proportion of deaths attributed to pneumonia and influenza was 6,7 %, which is below the epidemic threshold of 7,6 % for week 49. One state and territorial health department reported widespread influenza activity, one reported regional activity, 33 reported sporadic activity, and 14 reported no influenza activity**.

Laboratory Surveillance*:

During week 49, WHO and NREVSS laboratories reported 943 specimens tested for influenza viruses. Two influenza A (H3N2) viruses, 6 unsubtyped influenza A viruses, and 3 influenza B viruses were identified.

Since September 30, WHO and NREVSS laboratories have tested a total of 12 282 specimens for influenza viruses and 172 (1,4 %) were positive. Of the 172 isolates identified, 163 (95 %) were influenza A viruses and 9 (5 %) were influenza B viruses. One hundred and twelve (69 %) of the 163 influenza A viruses identified have been subtyped; 111 were influenza A (H3N2) viruses and one was an influenza A (H1N1) virus. Twenty-two states have reported laboratory-confirmed influenza. Influenza A (H3N2) isolates were identified in Alaska, Arizona, Colorado, Florida, Hawaii, New York, North Carolina, North Dakota, Pennsylvania, South Carolina, Texas, Utah, and Wisconsin; the influenza A (H1N1) isolate was identified in Washington; and unsubtyped influenza A isolates were identified in Alabama, Alaska, Colorado, Hawaii, Kansas, Louisiana, Minnesota, New York, Oregon, Texas, Virginia, Washington, Wisconsin, and West Virginia. Influenza B isolates were identified in Hawaii, Louisiana, Michigan, Texas, and Virginia. Eighty-eight (51 %) of the 172 influenza viruses isolated were identified in Alaska.

Influenza Virus Isolated
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Antigenic Characterization:

CDC antigenically characterized 10 influenza viruses collected in September and 23 collected in October: 30 influenza A (H3N2) viruses, 2 influenza A (H1N1) viruses, and 1 influenza B virus. All viruses were similar to the vaccine strains A/Panama/2007/99 (H3N2), A/New Caledonia/ 20/99 (H1N1), and B/Sichuan/379/99, respectively.

Pneumonia and Influenza (P&I) Mortality Surveillance:

During week 49, the percentage of all deaths due to pneumonia and influenza as reported by the vital statistics offices of 122 U.S. cities was 6,7 %. This percentage is below the epidemic threshold of 7,6 % for week 49.

Pneumonia And Influenza Mortality

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Influenza-like Illness Surveillance *:

During week 49, 1,2 % of patient visits to U.S. sentinel physicians were due to ILI. This is below the national baseline of 1,9 %. On a regional level, the percentage of visits for ILI ranged from 0,8 % to 3,9 %.*** Due to wide variability in regional level data, it is not possible to calculate region-specific baselines and it is not appropriate to apply the national baseline to regional level data.

Bar Chart for Influenza-like Illness
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Influenza Activity as Assessed by State and Territorial Epidemiologists**:

Influenza activity was reported as widespread in Alaska and regional in Colorado. Thirty-three states and Washington, DC reported sporadic activity, and 14 states and New York City reported no influenza activity. One state did not report.

U. S. map for Weekly Influenza Activity


* Reporting is incomplete for this week. Numbers may change as more reports are received.

** Influenza activity is defined as influenza-like illness and/or culture-confirmed influenza.

*** Surveillance Regions: New England (Connecticut, Maine, Massachusetts, New Hampshire, Vermont, Rhode Island); Mid-Atlantic (New Jersey, New York City, Pennsylvania, Upstate New York); East North Central (Illinois, Indiana, Michigan, Ohio, Wisconsin); West North Central (Iowa, Kansas, Minnesota, Missouri, Nebraska, North Dakota, South Dakota); South Atlantic (Delaware, Florida, Georgia, Maryland, North Carolina, South Carolina, Virginia, Washington, D.C., West Virginia); East South Central (Alabama, Kentucky, Mississippi, Tennessee); West South Central (Arkansas, Louisiana, Oklahoma, Texas); Mountain (Arizona, Colorado, Idaho, Montana, Nevada, New Mexico, Utah, Wyoming); Pacific (Alaska, California, Hawaii, Oregon, Washington)

Report prepared December 13, 2001

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